1. Field of the Invention
The present invention relates to a sheet processing apparatus which performs a process such as an alignment process for aligning edges of sheets, and an image forming apparatus including the sheet processing apparatus.
2. Description of the Related Art
There is known a system in which sheets are aligned using a conveying direction downstream edge (leading edge) of each sheet as an alignment reference in a sheet processing apparatus which performs a process, such as a binding process, after aligning the sheets. To handle various sheet sizes in this sheet processing apparatus, the position of a conveying direction upstream edge (trailing edge) of each of the aligned sheets varies depending on the sheet size. For this reason, it is necessary to take some measures to prevent a subsequent sheet from abutting against the trailing edge of the preceding aligned sheet and from slipping under the preceding sheet, for example.
As a solution to such a problem, a structure is disclosed in which a sufficient difference in height between a sheet aligning portion and a conveying portion which conveys sheets to the sheet aligning portion is ensured in a height direction. As another solution to the problem, there is disclosed a structure in which the sheet conveying portion is moved to the sheet aligning portion along a conveying direction according to the sheet size (U.S. Pat. No. 6,030,165), or a structure in which a reference member or a sheet processing portion is moved according to the sheet size. As still another solution to the problem, there is disclosed a structure in which large-size sheets are aligned using the leading edge thereof as a reference and small-size sheets are aligned using the trailing edge thereof as a reference, and a sheet bundle is then moved toward the leading edge reference (Japanese Patent Laid-Open No. 2001-348153).
However, the structure in which a sufficient difference in height between the sheet aligning portion and the conveying portion which conveys sheets to the sheet aligning portion is ensured in the height direction has a problem in that the size of the apparatus is increased in the height direction.
The structure for moving the conveying portion as disclosed in U.S. Pat. No. 6,030,165 and the structure for moving the alignment reference or the sheet processing portion require an actuator for moving such portions, leading to complication of the structure and an increase in cost. Furthermore, these structures require a space for moving such portions, leading to an increase in the size of the apparatus.
Also the structure disclosed in Japanese Patent Laid-Open No. 2001-348153 requires an actuator for moving such portions, leading to complication of the structure and an increase in cost. Additionally, the structure requires a space for moving such portions, leading to an increase in the size of the apparatus.